1. The Field of the Invention
The present invention relates generally to biodegradable polymer blends and articles manufactured therefrom. More particularly, the present invention relates to blends of two or more biopolymers and/or blends of biopolymers and fillers that yield sheets and films having improved physical properties, such as flexibility, elongation and/or dead-fold. The biodegradable polymer blends may be suitable for a number of applications, such as in the manufacture of disposable wraps, bags and other packaging materials or as coating materials.
2. The Relevant Technology
As affluence grows, so does the ability to purchase and accumulate more things. Never before in the history of the world has their been such a large number of people with such tremendous buying power. The ability to purchase relatively inexpensive goods, such as books, tools, toys and food, is a luxury enjoyed by virtually all levels of society, even those considered to be at the poorer end of the spectrum. Because a large percentage of what is purchased must be prepackaged, there has been a tremendous increase in the amount of disposable packaging materials that are routinely discarded into the environment as solid waste. Thus, as society becomes more affluent, it generates more trash.
Some packaging materials are only intended for a single use, such as boxes, cartons, pouches, bags and wraps used to package items purchased from wholesale and retail outlets. Even the advent of computers and “paperless” transactions has not stemmed the rising tide of packaging wastes. Indeed, the onset of “e-commerce” has spawned a great mail-order fad, thus creating a whole new market of individually packaged and shipped items.
Moreover, the modern, fast-paced lifestyle has greatly disrupted traditional eating routines in which people prepared their own meals and sat down as a family or group. Instead, people grab food on the run, thus creating ever-increasing amounts of fast food packaging materials that are used once and then discarded. In view of the high volume of disposable packaging materials being generated, some countries, particularly those in Europe, have begun to mandate either the recycling of fast food generated wastes or the use of packaging materials which are “biodegradable” or “compostable”. Environmental activists commonly pressure companies that generate solid waste. As a result, large fast food chains such as McDonald's have been essentially forced to discontinue the use of certain nonbiodegradable packaging materials such as foamed polystyrene, either by government fiat or by pressure by environmental groups. McDonald's currently uses a combination of paper wraps and cardboard boxes as an interim solution until more environmentally friendly packaging materials can be made on a commercial basis. There is therefore an ever-present need to develop biodegradable alternatives to nonbiodegradable paper, plastics and metals.
In response to the demand for more environmentally friendly packaging materials, a number of new biopolymers have been developed that have been shown to biodegrade when discarded into the environment. Some of the larger players in the biodegradable plastics market include such well-known chemical companies as DuPont, BASF, Cargill-Dow Polymers, Union Carbide, Bayer, Monsanto, Mitsui and Eastman Chemical. Each of these companies has developed one or more classes or types of biopolymers. For example, both BASF and Eastman Chemical have developed biopolymers known as “aliphatic-aromatic” copolymers, sold under the trade names ECOFLEX and EASTAR BIO, respectively. Bayer has developed polyesteramides under the trade name BAK. Du Pont has developed BIOMAX, a modified polyethylene terephthalate (PET). Cargill-Dow has sold a variety of biopolymers based on polylactic acid (PLA). Monsanto developed a class of polymers known as polyhydroxyalkanoates (PHA), which include polyhydroxybutyrates (PHB), polyhydroxyvalerates (PHV), and polyhydroxybutyrate-hydroxyvalerate copolymers (PHBV). Union Carbide manufactures polycaprolactone (PCL) under the trade name TONE.
Each of the foregoing biopolymers has unique properties, benefits and weaknesses. For example, biopolymers such as BIOMAX, BAK, PHB and PLA tend to be strong but are also quite rigid or even brittle. This makes them poor candidates when flexible sheets or films are desired, such as for use in making wraps, bags and other packaging materials requiring good bend and folding capability. In the case of BIOMAX, DuPont does not presently provide specifications or conditions suitable for blowing films therefrom, thus indicating that it may not be presently believed that films can be blown from BIOMAX and similar polymers.
On the other hand, biopolymers such as PHBV, ECOFLEX and EASTAR BIO are many times more flexible compared to the more rigid biopolymers discussed immediately above. However, they have relatively low melting points such that they tend to be self adhering and unstable when newly processed and/or exposed to heat. While initially easily blown into films, such films are often difficult to process on a mass scale since they will tend to self adhere when rolled onto spools, which is typically required for sale and transport to other locations and companies. To prevent self-adhesion (or “blocking”) of such films, it is typically necessary to incorporate a small amount (e.g. 0.15% by weight) of silica, talc or other fillers.
Another important criteria for sheets and films used in packaging is temperature stability. “Temperature stability” is the ability to maintain desired properties even when exposed to elevated or depressed temperatures, or a large range of temperatures, which may be encountered during shipping or storage. For example, many of the more flexible biopolymers tend to become soft and sticky if heated significantly above room temperature, thus compromising their ability to maintain their desired packaging properties. Other polymers can become rigid and brittle upon being cooled significantly below freezing (i.e., 0° C.). Thus, certain homopolymers or copolymers may not by themselves have sufficient stability within large temperature ranges.
In the case of the packaging of foods, such as refrigerated meats or fast foods, the packaging materials may be subjected to widely fluctuating temperatures, often being exposed to rapid changes in temperature. A biopolymer that may be perfectly suitable at room temperature, for example, may become completely unsuitable when used to wrap hot foods, particularly foods that emit significant quantities of hot water vapor or steam. In the case of meats, a wrapping that may be suitable when used at room temperature or below, such as at refrigeration or freezing temperatures, might become soft and sticky during microwave thawing of the meat. Of course, it would generally be unacceptable for a biopolymer to melt or adhere to the meat or fast food being served unless it was desired for some reason that the person actually consume the biopolymer.
Another factor that impacts whether a particular material is suitable for use as a wrap (e.g. sandwich or meat wrap) is whether sheets or films formed therefrom have suitable “dead-fold” properties. The term “dead-fold” is a measurement of the tendency of a sheet or film to remain in a desired orientation once used to encapsulate, enclose, wrap or otherwise enclose at least a portion of an item to be packaged. Wraps made from paper, for example, typically have modest to excellent dead fold properties depending on how the paper has been processed or treated. On the other hand, many plastic films or sheets (e.g. polyethylene) have very poor dead-fold properties such that they make very poor wraps. Instead, they are better suited for other uses, such as sacks, bags, pouches, coverings, etc. where good dead-fold is not necessary or desirable. In order to compensate for generally poor dead-fold properties, plastic wraps are typically manufactured to have high self-cling (e.g. SARAN WRAP). Self cling is a property having little to do with dead-fold, and is akin to the use of adhesives. One problem with self cling wraps is that they can be very difficult to handle. A self-cling wrap that is accidentally allowed to cling to itself before being used to wrap the substrate becomes useless and must be discarded and replaced with another length of self-cling wrap.
Paper also breathes (i.e. transmits gas) and has good water vapor transmission unless completely sealed with a wax or plastic. Plastic films and sheets, on the other hand, generally have very poor water vapor transmission and breathability. As a result, paper is a much better as a wrap for hot foods than plastic sheets because it permits the escape of water vapor. A plastic sheet, on the other hand, will retain virtually all of the water vapor, which condenses over time on the plastic surface and can make the food soggy, particularly a bun or slice of bread.
In view of the foregoing, it would be an advancement in the art to provide biodegradable polymers which could be readily formed into sheets and films that had strength and flexibility properties suitable for use as packaging materials and that had suitable temperature stability for a given use. In addition or alternatively, it would also be an advancement in the packaging art to provide improved biodegradable polymers that could be formed into sheets and films having sufficient dead-fold so that they could be folded, wrapped or otherwise manipulated in order to reliably enclose a substrate therein. In addition or alternatively, it would be a further advancement in the packaging art to provide improved biodegradable sheets and films that had enhanced breathability and water vapor transmission compared to conventional plastic sheets.
Such improved biopolymers, as well as sheets and films formed therefrom, are disclosed and claimed herein.